Description

The
mkstemp()
function generates a unique temporary filename from
template,
creates and opens the file,
and returns an open file descriptor for the file.

The last six characters of
template
must be "XXXXXX" and these are replaced with a string that makes the
filename unique.
Since it will be modified,
template
must not be a string constant, but should be declared as a character array.

The file is created with
permissions 0600, that is, read plus write for owner only.
The returned file descriptor provides both read and write access to the file.
The file is opened with the
open(2)
O_EXCL
flag, guaranteeing that the caller is the process that creates the file.

The
mkostemp()
function is like
mkstemp(),
with the difference that the following bits---with the same meaning as for
open(2)---may
be specified in
flags:
O_APPEND,
O_CLOEXEC,
and
O_SYNC.
Note that when creating the file,
mkostemp()
includes the values
O_RDWR,
O_CREAT,
and
O_EXCL
in the
flags
argument given to
open(2);
including these values in the
flags
argument given to
mkostemp()
is unnecessary, and produces errors on some
systems.

The
mkstemps()
function is like
mkstemp(),
except that the string in
template
contains a suffix of
suffixlen
characters.
Thus,
template
is of the form
prefixXXXXXXsuffix,
and the string XXXXXX is modified as for
mkstemp().

The
mkostemps()
function is to
mkstemps()
as
mkostemp()
is to
mkstemp().

Return Value

On success, these functions return the file descriptor
of the temporary file.
On error, -1 is returned, and
errno
is set appropriately.

Errors

EEXIST

Could not create a unique temporary filename.
Now the contents of template are undefined.

EINVAL

For
mkstemp()
and
mkostemp():
The last six characters of template were not XXXXXX;
now template is unchanged.

For
mkstemps()
and
mkostemps():
template
is less than
(6 + suffixlen)
characters long, or the last 6 characters before the suffix in
template
were not XXXXXX.

These functions may also fail with any of the errors described for
open(2).

Versions

mkostemp()
is available since glibc 2.7.
mkstemps()
and
mkostemps()
are available since glibc 2.11.

Attributes

The
mkstemp(),
mkostemp(),
mkstemps(),
and
mkostemps()
functions are thread-safe.

Conforming To

mkstemp():
4.3BSD, POSIX.1-2001.

mkstemps():
unstandardized, but appears on several other systems.

mkostemp()
and
mkostemps():
are glibc extensions.

Notes

In glibc versions 2.06 and earlier, the file is created with permissions 0666,
that is, read and write for all users.
This old behavior may be
a security risk, especially since other UNIX flavors use 0600,
and somebody might overlook this detail when porting programs.
POSIX.1-2008 adds a requirement that the file be created with mode 0600.

More generally, the POSIX specification of
mkstemp()
does not say anything
about file modes, so the application should make sure its
file mode creation mask (see
umask(2))
is set appropriately before calling
mkstemp()
(and
mkostemp()).

See Also

Colophon

This page is part of release 3.80 of the Linux
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A description of the project,
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and the latest version of this page,
can be found at
http://www.kernel.org/doc/man-pages/.

License & Copyright

Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
and Copyright (C) 2008, Michael Kerrisk
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References consulted:
Linux libc source code
Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
386BSD man pages
Modified Sat Jul 24 18:48:48 1993 by Rik Faith (faith@cs.unc.edu)
Modified 980310, aeb
Modified 990328, aeb
2008-06-19, mtk, Added mkostemp(); various other changes